nuclear chemistry.....aim 5

what are the risks and benefits associated with radioactivity?

.....aim 4

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HW From textbook “CHEMISTRY a Contemporary Approach”

 

There are inherent risks associated with radioactivity and the use of radioactive isotopes.

 

Fission reactions

Benefits:

Large amount of energy is released

Production of electricity in nuclear plants (20% of the electricity produced in the US comes from nuclear power)

Development of nuclear weapons (Atomic bomb, depleted uranium bullets)

Creations of new elements in accelerators (Americium-241 used in smoke detectors)

 

Risks:

Dangerous nuclear waste are produced

Accidents can released radiations in the environment

Fusion reactions

Benefits:

Release of larger amount of energy than fission. However, they are not a practical source of energy because the technical problems of high temperature, pressure, and containment of reaction are enormous.

 

Risks:

Relatively low

Biological exposure

Radiation damage to living organisms results from the ability of energetic particles and photons to ionize atoms and break chemical bonds.

Example

The irradiation of water produces ions and free radicals such as H*, *OH, and H2O+ which can damage cells.

Radiation damage can be genetic or somatic. Genetic damage affects genes and can be inherited while somatic damage affects molecules which can interfere with cell functions such as growth and division.

Example

Impaired production of red blood cells and antibodies results in anemia and increased risk of infection.

Long-term storage and disposal

At the present, there are no permanent storage facilities for nuclear waste. The following are ways we deal with it.

Nuclear accidents

Example

The Chernobyl disaster in Ukraine in 1986 occurred when the graphite moderator caught on fire. The reactor did not have an adequate external shield. 31 people died and tens of thousands are expected to develop cancers over the next 50 years. Closed in 2000.

 

Example

In 1979 water pump failure and human error resulting in overheating and partial meltdown of fuel rods at the Three Mile Island nuclear reactor in Pennsylvania.

Radioactive isotopes have many beneficial uses.

 

radioactive dating

Example

Carbon dating using C-14 is used to find the approximate age of organic samples.

Step 1:

14

 

 

1

 

 

14

 

 

 1

 

 

N

+

 

n

-->

 

C

+

 

H

7

 

 

0

 

 

 6

 

 

 1

 

 

 

(from cosmic rays)

 

 

 

 

 

 

Step 2:  14C combines with O2  to form 14CO2: 14C + O2  --> 14CO2

Step 3: 14CO2 enters plants: 14CO2 --> photosynthesis --> 14C in plants

Step 4: 14CO2 enters animals: 14C in plants --> 14C in animals

Step 5: As 14C decays  it changes into 14N. In time, the ratio 14C to 12C becomes constant in all living matter.

Step 6: When a living thing dies the supply of 14C is cut off since it can no longer utilize CO2 therefore, the 14C / 12C ratio decreases. Thus, a piece of bone or wood buried in the ground for centuries contains fewer 14C radioisotopes than does a fresh piece.

Geology

Example

U-238 is used for dating rocks. U-238 (half-life of 4.5 billion years) decays to lead-206. The ratio of U-238 to Pb-206, present in a rock, can be used to determine the age of a rock.

Tracing chemical

Example

Vitamin B 12 can be tagged with a radioisotope of cobalt to study the absorption of the vitamin from the gastrointestinal tract.

 

Example

Compounds tagged with Fe-59 and Fe-55 are used to study the absorption of iron.

 

Example

Glucose tagged with carbon-11 (half-life, 20.3 minutes and positron decay mode) circulates through the body, and the positrons emitted in the heart, brain or some other organ are monitored by a PET detector. A computer uses this information to construct an image (called a PET scan) of the organ that is being examined. PET scans have been used to study the effects of drugs on cancers, to measure damage in victims of stroke or heart attack, and to study chemical changes that occur during epileptic seizures.

Biological processes

Example

Melvin Calvin, a biochemist, labeled CO2  with C-14 and worked out the process by which plants photosynthesize carbohydrate from CO2 and H2O

 

Example

In food production, radiations are used to kill bacteria, yeasts, molds, and insect eggs, allowing foods to be stored for longer periods of time.

Industrial measurement

Radioisotopes are used to determined the thickness of metal sheets, plastic wrap, and other products. The thickness of these products is calculated according to the intensity of penetration of radiations.

 

Nuclear power

They are used in nuclear plants, in transportation, and in weapons (A and H-bombs and depleted uranium bullets tips)

 

Detection of disease

Only radioisotopes with very short half-lives that can be quickly eliminated from the body are used. Their use in therapy or diagnosis is based on their tendency to concentrate in specific areas of the body.

Example

Iodine-131, a beta emitter, is taken as sodium iodide in drinking water. Almost all of it will find its way to the thyroid. The rate of iodine-131 uptake, determined with a Geiger counter or other scanning device, indicates whether the thyroid glands are functioning properly.

 

Example

Sodium chloride containing sodium-24, can be injected into the bloodstream to study blood circulation. The beta particles emitted by the sodium-24 are followed and an impaired circulation is immediately detected.

 

Example

A thallium-201 compound injected into the bloodstream will concentrate in normal heart muscle but will not remain in damaged tissue. A photograph with a nuclear scintillation camera allows the physician to locate the damaged areas.

 

Example

Technetium-99m is used for locating brain tumors and damaged heart cells.Technetium-99m is probably the most widely used radioisotope in medicine today; it is a decay product, of molybdenum-99.

Treatment of disease

Example

Radium-226 and cobalt-60 are used in cancer therapy.

TEST YOUR UNDERSTANDING

6/07

50 Which radioisotope is used in medicine to treat thyroid disorders?     (1) cobalt-60     (2) iodine-131     (3) phosphorus-32     (4) uranium-238

1/06

50 The decay of which radioisotope can be used to estimate the age of the fossilized remains of an insect?     (1) Rn-222 (2) I-131 (3) Co-60 (4) C-14

1/05

Base your answers to questions 82 through 84 on the information below, the Reference Tables for Physical Setting/Chemistry, and your knowledge of chemistry.

Radioactivity and radioactive isotopes have the potential for both benefiting and harming living organisms. One use of radioactive isotopes is in radiation therapy as a treatment for cancer. Cesium-137 is sometimes used in radiation therapy.

A sample of cesium-137 was left in an abandoned clinic in Brazil in 1987. Cesium-137 gives off a blue glow because of its radioactivity. The people who discovered the sample were attracted by the blue glow and had no idea of any danger. Hundreds of people were treated for overexposure to radiation, and four people died.

 

82 Using Reference Table N, complete the equation provided in your answer booklet for the radioactive decay of 137-Cs. Include both atomic number and mass number for each particle.

83 If 12.5 grams of the original sample of cesium-137 remained after 90.69 years, what was the mass of the original sample? 

84 Suppose a 40-gram sample of iodine-131 and a 40-gram sample of cesium-137 were both abandoned in the clinic in 1987. Explain why the sample of iodine-131 would not pose as great a radiation risk to people today as the sample of cesium-137 would. 

1/04

Base your answers to questions 71 through 74 on the article below.

Radioactivity at home

                You may be surprised to learn that you do not need to visit a nuclear power plant or a hospital X-ray laboratory to find sources of radioactivity. They are all around us. In fact, it is likely that you'll find a few at home. Your front porch may incorporate cinder blocks or granite blocks. Both contain uranium. Walk through the front door, look up, and you'll see a smoke detector that owes its effectiveness to the constant source of alpha particle emissions from Americium-241. As long as the gases remain ionized within the shielded container, electricity flows, and all is calm. When smoke enters the chamber, it neutralizes the charges on these ions. In the absence of these ions, the circuit breaks and the alarm goes off.

                Indicator lights on your appliances may use Krypton-85; electric blankets, promethium-147; and fluorescent lights, thorium-229. Even the food we eat is radioactive. The more potassium-rich the food source, the more potassium-40 (a radioactive isotope that makes up about 0.01% of the natural supply of this mineral) is present. Thus, brazil nuts, peanuts, bananas, potatoes, and flour, all rich in potassium, are radiation sources.

-Chem Matters

 April 2000

71 Write the equation for the alpha decay that occurs in a smoke detector containing Americium-241 (Am-241).

72 How is the radioactive decay of Krypton-85 different from the radioactive decay of Americium-241?
73 State one benefit or useful application of radioactivity not mentioned in this article. 
74 State one risk or danger associated with radioactivity.

1/03

1 According to Table N, which radioactive isotope is best for determining the actual age of Earth? (1) U-238    (2) Sr-90   (3) Co-60  (4) C-14

2  Which statement explains why nuclear waste materials may pose a problem?

(1) They frequently have short half-lives and remain radioactive for brief periods of time.

(2) They frequently have short half-lives and remain radioactive for extended periods of time.

(3) They frequently have long half-lives and remain radioactive for brief periods of time.

(4) They frequently have long half-lives and remain radioactive for extended periods of time.

8/03

Base your answers to questions 70 through 72 on the article below.
                In the 1920s, paint used to inscribe the numbers on watch dials was composed of a luminescent (glow-in-the-dark) mixture. The powdered-paint base was a mixture of radium salts and zinc sulfide. As the paint was mixed, the powdered base became airborne and drifted throughout the workroom causing the contents of the workroom, including the painters' clothes and bodies, to glow in the dark.

                The paint is luminescent because radiation from the radium salts strikes a scintillator. A scintillator is a material that emits visible light in response to ionizing radiation. In watch-dial paint, zinc sulfide acts as the scintillator.
                Radium present in the radium salts decomposes spontaneously, emitting alpha particles. These particles can cause damage to the body when they enter human tissue.
Alpha particles are especially harmful to the blood, liver, lungs, and spleen because they can alter genetic information in the cells. Radium can be deposited in the bones because it substitutes for calcium.
70 Write the notation for the alpha particles emitted by radium in the radium salts.

71 How can particles emitted from radioactive nuclei damage human tissue?
72 Why does radium substitute for calcium in bones?

8/02

a) State one possible advantage of using nuclear power instead of burning fossil fuels.

b) State one possible risk of using nuclear power.

c) If animals feed on plants that have taken up Sr-90, the Sr-90 can find its way into their bone structure. Explain one danger to the animals.

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